Buy an adustable length pushrod to check and see the size you need. They sell them through summit for about 11 bucks... i use the crane cams one that goes from about 6.1 in to 6.45.... or something close to that.....The length i had to use on mine were 6.125....that is a bit smaller than stock but the block and heads have had alot taken off.....It can vary by alot.
I would really check the length first...i used the stock 6.250 length on mine back when it was a stock block and brand new heads and messed up 16 valves in 5000 miles....it then cost me 500 bucks in machine work and new valves to correct the problem....and it all could have been avoided with a damn 12 adustable pushrod. EVERY combination is different....even if you just have different rockers then another guy it can through it off enough to cause damage. CHECK IT!!!!